Thin film deposition as an active conductor and method therefor

ABSTRACT

A method includes populating components in a cavity of a substrate, disposing a polymer over the components and within the cavity. The polymer is cured and a thin film is formed on the polymer. In addition, a method includes forming an EMI shield within a medical device by depositing a thin film of metal on a surface within the medical device. The thin film of metal, of gold, aluminum, or copper, is formed by vapor deposition or sputtering. An apparatus includes a first substrate assembly including a first substrate having a cavity. A first set of electronic components are disposed within the cavity, and a first polymer is disposed over the first set of components. Deposited on an outer surface of the first polymer by vapor deposition is a thin film of metal. The thin film of metal is electrically coupled with a ground. A second substrate assembly including a second substrate is coupled with the first substrate assembly.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application is a division of U.S. patent application Ser.No. 09/499,725, filed on Feb. 8, 2000, the specification of which isincorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to electronics devicesemploying thin film deposition as an active conductor. Moreparticularly, it pertains to medical devices such as an implantablepulse generator

BACKGROUND OF THE INVENTION

[0003] Pulse generators such as pacemakers or defibrillators areimplanted in the body for electrical cardioversion and/or pacing of theheart. Electrodes, which are used to apply electrical energy, arecoupled with the pulse generator and are implanted in or about theheart. The electrodes are used to reverse (i.e., defibrillate orcardiovert) certain life threatening arrhythmias, or to stimulatecontraction (pacing) of the heart. Electrodes have also been used tosense near the sinal node in the atrium of the heart and to deliverpacing pulses to the atrium.

[0004] A pulse generator is implanted during a surgical procedure underthe skin of an individual. One desirable characteristic of such a deviceis that it has a relatively small volume or size. This is to increasethe comfort to the patient, to prevent protrusion of the device frombeneath the skin, and to prevent interference of the device withadjacent vital organs of the individual. One way to reduce the size ofthe pulse generator is to utilize small electronic components within thedevice, and to place the small electronic components closer together onthe substrate. In addition, integrated circuit chip carriers are used toattach integrated circuits to circuit boards. The chip carriers allowfor high density and complex interconnections between the integratedcircuit and the circuit board.

[0005] When electronic components are placed closer together and/orcomplex interconnections are implemented, sensitive electronic circuitryand components are susceptible to electromagnetic interference (EMI)emanating from other circuits and components. One way to address theproblem of EMI is to incorporate EMI shields to isolate the sensitivecircuits from other circuits. The EMI shields are in the form of aseparate piece of conductive tape or foil which is incorporated into theimplantable device. The physical size of the foil limits efforts toreduce the overall size of the device, since the separate componentconsumes valuable space and volume within the implantable device.

[0006] In addition, electrical connections between the small electroniccomponents must be made. Electrically conductive conduits are used tomake electrical and mechanical connections between various circuits anddiscrete components in implantable defibrillators and pacemakers. Oneexample of making such connections is metalized high temperature ceramic(HTCC) or metalized low temperature ceramic (LTCC). However, LTCC andHTCC technologies require screen printing specific traces on numerousspecific ceramic layers followed by a high pressure lamination andelevated temperature (e.g. 850 degrees Celsius) to create a substrate ofalternative conductors and insulators, which can be harmful totemperature sensitive components. Alternatively, printed circuit boardsare another option. However, the printed circuit boards typically useetched copper foil which is laminated to a rigid organic fiber board ina multi layer arrangement using a variety of adhesive permanentlybinding the multi-layers together.

[0007] Accordingly, there is a need for reducing the overall size of theimplantable device. There is also a need for an implantable medicaldevice which simplifies the interconnect routing between the variouselectronic components of the device. Furthermore, there is a need toreduce EMI of the implantable medical device.

SUMMARY OF THE INVENTION

[0008] A method includes populating components in a cavity of asubstrate, and disposing a polymer over the components within thecavity. The polymer is cured and a thin film of metal is formed on thepolymer, where the polymer may have a non-planar surface on which thethin film of metal is deposited. The thin film of metal is vapordeposited on the polymer. Alternatively, the thin film of metal issputtered on the polymer. The thin film of metal optionally includes athin film of metal of the following materials: gold, aluminum, orcopper. Optionally, the method includes electrically coupling the thinfilm of metal with an electrical ground. In another embodiment, theabove assembly is coupled with a second substrate assembly, and the thinfilm is disposed between the two assemblies.

[0009] An alternative method includes forming an EMI shield within amedical device, where forming the EMI shield comprises depositing a thinfilm of metal on a surface within the medical device. In one embodiment,depositing the thin film of metal includes vapor depositing metal on thesurface. Alternatively, depositing the thin film of metal includessputtering metal on the surface. In another embodiment, the thin film isdeposited on an insulator disposed within a case. The thin film of metaloptionally includes a thin film of metal of the following materials:gold, aluminum, or copper. Optionally, the method includes electricallycoupling the thin film of metal with an electrical ground. In anotheralternative, the EMI shield is formed by depositing the thin film ofmetal over insulation disposed over a resistor.

[0010] An apparatus is also provided herein where the apparatus includesa first substrate assembly including a first substrate having a cavity.A first set of electronic components are disposed within the cavity, anda first polymer is disposed over the first set of components. Depositedon an outer surface of the first polymer by vapor deposition is a thinfilm of metal. The thin film of metal electrically coupled with aground. A second substrate assembly including a second substrate iscoupled with the first substrate assembly. Optionally, the outer surfaceof the first polymer is non-planar. In another embodiment, the apparatusfurther includes a case having an insulator disposed therein. The firstsubstrate assembly and the second substrate assembly are disposedbetween the insulator and the case, and a thin film of metal is vapordeposited on at least a portion of the insulator.

[0011] The method and structure described herein do not use or requireany heat generation to deposit the thin film and/or conductiveinterconnects. In addition, the method can be used on a wide variety ofmaterials while maintaining adequate adhesion and conduction sufficientfor use in an implantable medical device such as a defibrillator orpacemaker. Further, the surface on which the traces are deposited is notlimited in geometry or topography. Since the thin film does not requirehigh temperature during the deposition or sputtering process, thecomponents which populate the substrate will not be harmed by hightemperatures. In addition, since the thin film layer can be depositedvery thin, the size of the medical device is not unnecessarilyincreased.

[0012] These and other embodiments, aspects, advantages, and features ofthe present invention will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the art byreference to the following description of the invention and referenceddrawings or by practice of the invention. The aspects, advantages, andfeatures of the invention are realized and attained by means of theinstrumentalities, procedures, and combinations particularly pointed outin the appended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is an exploded perspective view illustrating a substrateassembly constructed in accordance with one embodiment.

[0014]FIG. 2A is a perspective view illustrating an assembled substrateassembly constructed in accordance with one embodiment.

[0015]FIG. 2B is a cross-sectional view of FIG. 2A taken along 2B-2B.

[0016]FIG. 3 is an exploded perspective view illustrating a substrateassembly constructed in accordance with another embodiment.

[0017]FIG. 4A is a perspective view illustrating an assembled substrateassembly constructed in accordance with one embodiment.

[0018]FIG. 4B is an exploded cross-sectional view of FIG. 4A taken along4B-4B.

[0019]FIG. 5 is an exploded perspective view illustrating an implantablemedical device constructed in accordance with another embodiment.

[0020]FIG. 6 is a cross-sectional view illustrating an implantablemedical device constructed in accordance with an embodiment.

[0021]FIG. 7 is a cross-sectional view illustrating an implantablemedical device constructed in accordance with an embodiment.

DESCRIPTION OF THE EMBODIMENTS

[0022] In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that other embodiments may be utilized and that structuralchanges may be made without departing from the scope of the presentinvention. Therefore, the following detailed description is not to betaken in a limiting sense, and the scope of the present invention isdefined by the appended claims and their equivalents.

[0023]FIGS. 1, 2A and 2B illustrate a substrate assembly 100 for use ina medical device, for instance, an implantable pulse generator. Thesubstrate assembly 100 includes a substrate 110 having multiplecomponents 118 disposed thereon. The substrate 110 has a cavity 112therein, and the components 118 are populated on the substrate 110within the cavity 112. The cavity 112 is filled with a dielectricpolymer 114, where the polymer 114 is disposed over the components 118to cover and insulate the components 118. In addition, the polymer 114protects the components 118. One example of a suitable polymer is anepoxy. Other suitable materials include those which fill the voids orspaces amongst the components and which solidifies or becomessubstantially rigid when cooled. The material should also have adequatecompressive strength, and should also be lightweight. The polymer 114assists in providing insulation between the components 118, and providesrelatively high strength when it is cured. After the polymer 114 isdisposed within the cavity 112, the polymer is cured at about 150degrees C. to form a rigid to semi-rigid structure.

[0024] The polymer 114 is defined in part by an outer surface 122. Athin film metal is vapor deposited on the outer surface 122 of thepolymer 114 to form a thin film 130, as shown in FIGS. 2A and 2B. Todeposit the thin film metal, the atoms or molecules from a vaporizationsource reach the outer surface 122 of the polymer 114 without collidingwith residual gas molecules. The vaporization source comprises one thatthermally vaporizes materials, for example by evaporation orsublimation. Vacuum evaporation allows for a deposit of thin film of avariety of materials which can be deposited at high rates over largeareas in a very pure form. The thin film 130 at least partially coversthe outer surface 122, and optionally covers the entire outer surface122 of the polymer 114. Alternatively, the thin film metal is sputteredon to the outer surface 122 to form a thin film 130. In contrast to thevapor deposition process which depends on heat to vaporize the material,sputtering is an atom-by-atom process. A target is bombarded by ionswhich physically chip atoms off of the target, causing them to beejected from the target and subsequently strike the outer surface 122and adhere thereto. The atoms build up on the second surface 122 to forma layer of material, resulting in the thin film 130. It should be notedthat the thin film 130 can be formed on the outer surface 122 prior tothe polymer 114 being fully cured, or can be formed on the outer surface122 after the polymer 114 is fully cured. Further, the outer surface 122is optionally non-planar. In one embodiment, the thin film 130 is formedto a thickness of about 25 microns. The thin film 130 is electricallycoupled with a ground pin 132, as shown in FIG. 2B, such that the thinfilm 132 can be used for electrical isolation. The thin film 130 isformed from a variety of conductive materials including, but not limitedto, gold, aluminum, or copper.

[0025]FIGS. 3, 4A and 4B illustrate another embodiment, and shows asubstrate assembly 200 including a first substrate assembly 202 and asecond substrate assembly 204. The first substrate assembly 202 includesa first substrate 210 having multiple components 220 disposed thereon.The multiple components 220, include, but are not limited to, at leastone integrated circuit. The first substrate 210 has a cavity 212therein, and the components 220 are populated on the substrate 210within the cavity 212. The cavity 212 is filled with a dielectricpolymer 214, where the polymer 214 is disposed over the components 220to cover and insulate the components 220. In addition, the polymer 214protects the components 220. One example of a suitable polymer is anepoxy. Other suitable materials include those which fill the voids orspaces amongst the components and which solidifies or becomessubstantially rigid when cooled. The material should also have adequatecompressive strength, and should also be lightweight. After the polymer214 is disposed within the cavity 212, the polymer is cured at about 150degrees C. to form a rigid to semi-rigid structure.

[0026] The polymer filling 214 is defined in part by an outer surface218. A thin film metal is vapor deposited on the outer surface 218 ofthe polymer 214 to form a thin film 230, as shown in FIG. 4B.Alternatively, the thin film metal is vacuum deposited on the outersurface 218. To deposit the thin film metal, the atoms or molecules froma vaporization source reach the outer surface 218 of the polymer 214without colliding with residual gas molecules. The vaporization sourcecomprises one that thermally vaporizes materials, for example byevaporation or sublimation. Vacuum evaporation allows for a deposit ofthin film of a variety of materials which can be deposited at high ratesover large areas in a very pure form.

[0027] The thin film 230 at least partially covers the outer surface218, and optionally covers the entire outer surface 218 of the polymer214. Alternatively, the thin film metal is sputtered on to the outersurface 218 to form the thin film 230. It should be noted that the thinfilm 230 can be formed on the outer surface 218 prior to the polymer 214being fully cured, or can be formed on the outer surface 218 after thepolymer 214 is fully cured. The thin film is formed from a variety ofconductive materials including, but not limited to, gold, aluminum, orcopper. In one embodiment, the thin film 230 is formed to a thickness ofabout 25 microns. Optionally, the thin film 230 is electrically coupledwith an electrical contact 232, as shown in FIG. 4B, such that the thinfilm 230 can be used for electrical isolation, and/or the thin film 230forms a shield against EMI. Optionally, the electrical contact 232 iselectrically coupled with a ground pin. Connecting the thin film 232with ground electrically isolates the first substrate assembly 202 fromthe second substrate assembly 204.

[0028] The first substrate assembly 202 is coupled with the secondsubstrate assembly 204, as shown in FIG. 4A, such that the firstsubstrate assembly 202 is electrically isolated from the secondsubstrate assembly 204. The second substrate assembly 204 includes asecond substrate 250 having multiple components 260 disposed thereon.The multiple components 260, include, but are not limited to, at leastone integrated circuit. The second substrate 250 has a cavity 252therein, and the components 260 are populated on the second substrate250 within the cavity 252. The cavity 252 is filled with a dielectricpolymer 254, where the polymer 254 is disposed over the components 260to cover and insulate the components 260. The polymer 254 is disposed onand/or within the second substrate 250 as discussed above for the firstsubstrate assembly 202.

[0029]FIG. 5 illustrates an exploded medical device 300, such as animplantable pulse generator. The medical device 300 has a clamshell typecase 310 having a pair of confronting concave halves 312 which, whenmated, define a perimeter parting line 314. The confronting concavehalves 312 are formed from a number of electrically conductive materialssuch as titanium, stainless steel or other bio-compatible material. Theparting line 314 is sealed, for example by laser welding, to completelyseal the electronic components within the enclosure or case.

[0030] The case 310 hermetically seals electronics, discussed furtherbelow, within the case in an airtight environment. Since the case 310 issealed, the electronics are not damaged by contact with body fluids whenthe device is used subcutaneously in an individual. The case 310 alsoassists in providing structural integrity for the device to protect theelectrical components held within the case 310. The case 310 must notdeform or collapse when subjected to external compression forces duringmanufacture of the device, during an implant procedure, and onceimplanted within an individual.

[0031] Disposed within the case 310 are electronics including electroniccomponents 306 and also the substrate assembly 200 including a firstsubstrate assembly 202 and a second substrate assembly 204. The firstsubstrate assembly 202 is coupled with the second substrate assembly 204(FIG. 4A). Optionally, the first substrate assembly 202 is coupled withthe second substrate assembly 204, such that the first substrateassembly 202 is electrically isolated from the second substrate assembly204. The second substrate assembly 204 includes a second substrate 250having multiple components 260 disposed thereon, as discussed above.

[0032] The first substrate assembly 202 includes a first substrate 210having multiple components 220 disposed thereon, as discussed above. Thefirst substrate 210 includes the polymer filling 214, which is definedin part by an outer surface 218 (FIG. 4B). Optionally, a thin film metalis vapor deposited on the outer surface 218 of the polymer 214 to form athin film 230, as shown in FIG. 4B. The thin film 230 at least partiallycovers the outer surface 218, and optionally covers the entire outersurface 218 of the polymer 214. Alternatively, the thin film metal issputtered on to the outer surface 218 to form the thin film 230. Thethin film is formed from a variety of conductive materials including,but not limited to, gold, aluminum, or copper.

[0033] The thin film 230 is electrically coupled with an electricalcontact 232, as shown in FIG. 4B, such that the thin film 232 can beused for electrical isolation. Optionally, the electrical contact 232 iselectrically coupled with a ground pin. Connecting the thin film 232with ground electrically isolates the first substrate assembly 202 fromthe second substrate assembly 204.

[0034] Referring again to FIG. 5, at least one insulator 330 is disposedwithin the case 310. The insulator 330 is formed of a non-conductivematerial, for instance, a non-conductive polymer. The insulator 330 isdisposed between one of the electrically conductive clamshell halves 312and the substrate assembly 200. Optionally, an insulator 330 is disposedadditionally or alternatively between one of the clamshell halves 312and the electronic components 306. The insulator 330 is defined in partby a first surface 332 which is disposed proximate to one of theclamshell halves 312, and a second surface 334 which is disposedproximate to the second substrate assembly 200 or the electroniccomponents 306.

[0035] A thin film metal is vapor deposited on at least a portion of thesecond surface 334 of the insulator 330, as shown in greater detail inFIG. 6 to form a layer of thin film 340. To deposit the thin film metal,the atoms or molecules from a vaporization source reach the secondsurface 334 of the insulator 330 without colliding with residual gasmolecules. The vaporization source comprises one that thermallyvaporizes materials, for example by evaporation or sublimation. Vacuumevaporation allows for a deposit of thin film of a variety of materialswhich can be deposited at high rates over large areas in a very pureform. The thin film 340 at least partially covers the second surface334, and optionally covers the entire second surface 334 of theinsulator 330.

[0036] Alternatively, the thin film metal is sputtered on to the secondsurface 334 to form a thin film 340. In one embodiment, the thin film340 is formed to a thickness of about 1 micron. Alternatively, the thinfilm 340 is formed to a thickness of up to about 25 microns. In contrastto the vapor deposition process which depends on heat to vaporize thematerial, sputtering is an atom-by-atom process. A target is bombardedby ions which physically chip atoms off of the target, causing them tobe ejected from the target and subsequently strike the second surface334 and adhere thereto. The atoms build up on the second surface 334 toform a layer of material, resulting in the thin film. The thin film isformed from a variety of conductive materials including, but not limitedto, gold, aluminum, or copper.

[0037] It should be noted that the thin film 340 can be formed on thesecond surface 334 of the insulator 330 to form trace lines such that itcan be used for electrical routing connections. For example, in formingthe thin film 340, a part of the second surface 334 is masked off, suchas with photoresist. Photoresist is a photosensitive coating that isapplied to a laminate and subsequently exposed through a film. Thephotoresist is developed resulting in a pattern that can be eitherplated or etched with the thin film 340. The etched or plated thin film340 forms trace lines, where the trace lines can be used for electricalconnections, for example, between components. Alternatively, the thinfilm 340 is electrically connected with the substrate assembly 200, suchthat the thin film 340 is electrically coupled with a ground pin and thethin film 340 electrically isolates the substrate assembly 200 from theconductive case 310.

[0038]FIG. 7 illustrates another embodiment, including a substrate 400having an electronic component 404. For instance, a resistor 410 isprinted on the substrate and fired. Disposed over the resistor 410 is aninsulator 420. Optionally, an overglaze 422 of insulating material isdisposed over the insulator 420. A thin film metal is vapor deposited onat least a portion of the insulator 420, to form a layer of thin film440. To deposit the thin film metal, the atoms or molecules from avaporization source reach the insulator 420 without colliding withresidual gas molecules. The vaporization source comprises one thatthermally vaporizes materials, for example by evaporation orsublimation. Vacuum evaporation allows for a deposit of thin film of avariety of materials which can be deposited at high rates over largeareas in a very pure form. The thin film 440 at least partially coversthe insulator 420, and optionally covers the entire insulator 420.Alternatively, the thin film metal is sputtered on to the insulator toform a thin film 440. In one embodiment, the thin film 440 is formed toa thickness of about 1 micron. Alternatively, the thin film 440 isformed to a thickness of up to about 25 microns. The thin film is formedfrom a variety of conductive materials including, but not limited to,gold, aluminum, or copper. The thin film 440 is electrically coupledwith an electrical contact 426, such that the electronic component 404can be electrically isolated from surrounding components.

[0039] Advantageously, the above described method and apparatus does notuse or require any heat generation to deposit the thin film and/orconductive interconnects. In addition, the method can be used on a widevariety of materials while maintaining adequate adhesion and conductionsufficient for use in an implantable medical device such as adefibrillator or pacemaker. Further, the surface on which the traces aredeposited is not limited in geometry or topography. Since the thin filmdoes not require high temperature during the deposition or sputteringprocess, the components which populate the substrate will not be harmedby high temperatures. In addition, since the thin film layer can bedeposited very thin, the size of the medical device is not unnecessarilyincreased. Significant size reductions, material savings and substantialweight savings may be achieved utilizing the implantable medical deviceof the invention.

[0040] It is to be understood that the above description is intended tobe illustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. An apparatus comprising: a first substrateassembly including a first substrate having a cavity therein, a firstset of electronic components disposed within the cavity, a first polymerdisposed over the first set of components, the first polymer having anouter surface, a thin film of metal vapor deposited on the outersurface, the thin film of metal electrically coupled with a ground; anda second substrate assembly including a second substrate, the secondsubstrate having electronic components disposed thereon, the secondsubstrate assembly being coupled with the first substrate assembly. 2.The apparatus as recited in claim 1, wherein the outer surface of thefirst polymer is non-planar.
 3. The apparatus as recited in claim 1,further comprising a clam shell case having an insulator disposedtherein, where the first substrate assembly and the second substrateassembly are disposed between the insulator and the clam shell case, anda thin film of metal is vapor deposited on at least a portion of theinsulator.
 4. An apparatus comprising: a substrate having one or moreelectronic components; a dielectric material covering the one or moreelectronic components; and an EMI shield, the EMI shield including afilm of metal on a surface of the dielectric material.
 5. The apparatusof claim 4, wherein the apparatus includes an outer shell and thesubstrate is disposed within the outer shell, wherein an insulator isdispose within the outer shell and there is a film of metal on a surfaceof the insulator.
 6. The apparatus of claim 4, firther comprising asecond substrate holding one or more electronic components, wherein thefilm of metal is located between the first substrate and the secondsubstrate.
 7. The apparatus of claim 4, wherein the film of metal iscoupled to an electrical ground.
 8. The apparatus of claim 4, whereinthe film of metal is gold, copper, or aluminum.
 9. The apparatus ofclaim 4, wherein a surface of the dielectric material is non-planar. 10.The apparatus of claim 4, wherein the film layer has a thickness of upto about 25 microns.
 11. The apparatus of claim 4, wherein the substrateincludes a cavity and the one or more electronic components are locatedwithin the cavity.
 12. An apparatus comprising: a first substrate havinga first set of electronic components disposed on the substrate, a firstpolymer disposed over the first set of components, the first polymerhaving an outer surface, a thin film of metal located on the outersurface, the thin film of metal electrically coupled with a ground; anda second substrate assembly including a second substrate, the secondsubstrate having electronic components disposed thereon, the secondsubstrate assembly being coupled with the first substrate assembly suchthat the thin film of metal is between the electronics components on thefirst substrate and the electronic components on the second substrate.13. The apparatus as recited in claim 12, wherein the outer surface ofthe first polymer is non-planar.
 14. The apparatus as recited in claim12, further comprising a clam shell case having an insulator disposedtherein, where the first substrate assembly and the second substrateassembly are disposed between the insulator and the clam shell case, anda thin film of metal is vapor deposited on at least a portion of theinsulator.
 15. An apparatus comprising: an electrically conductive case;a substrate assembly located within the case, the substrate assemblyhaving one or more electronic components; and an insulator disposedwithin the case between the case and the substrate assembly, wherein asurface of the insulator has a film of metal deposited on at least aportion of the surface.
 16. The apparatus of claim 15, wherein the filmcovers an entire surface of the insulator.
 17. The apparatus of claim15, wherein the film has a thickness of about 1 micron.
 18. Theapparatus of claim 15, wherein the film has a thickness of up to 25microns.
 19. The apparatus of claim 15, wherein the film of metalcomprises trace lines on the surface of the insulator such that thetrace lines are usable as electrical connections.
 20. The apparatus ofclaim 15, wherein the film of metal is connected to a ground pin suchthat the film electrically isolates the substrate assembly from theconductive case.